Leslie fhazer



Patented Jan. 21, 1947 METHOD OF PREPARING 'UNSATURATED NITRO COMPOUNDS Marvin H. Gold, Chicago, Ill., assignor to The Visking Corporation, Chicago, 111., a corporation of Virginia 3 Claims.

This invention relates to a process for preparing unsaturated nitro compounds. More particularly, it relates to a continuous process for preparing nitro olefins.

Unsaturated nitro compounds have been prepared heretofore by several methods. One of these methods involves refluxing of the nitro ester in an anhydrous solvent, such as ether or benzene, with an anhydrous alkaline carbonate or bicarbonate for several hours. In such a process the amount of materia1 which can be made in a given period of time is limited. Further, due to prolonged contact with the alkaline carbonate or bicarbonate, a large percentage of the lower molecular weight nitro olefins is polymerized during the period of reaction.

United States Patent 2,257,980 discloses a process of preparing unsaturated nitro compounds by the reaction of alkaline substances, such as alkali metal carbonates, with O-acylated-chydroxy nitro compounds, the alkali metal carbonate being in an amount which is below the stoichiometric amount. This process is also batch process and a relatively long period of time is required for the completion of the reaction.

United States Patent 2.298375 discloses a process of producing unsaturated nitro compounds by a one-stage process involving the union of formaldehyde with a nitro hydrocarbon or derivatives with a simultaneous splitting off of water. Though thi process is disclosed as being capable of being practiced in a continuous manner, nevertheless the yields are exceedingly small so as to make the process impractical. Additionally, due to the fact that in the reaction a molecule 'of water is formed for every molecule of nitro olefin, the process is of particular disadvantage in the production of lower nitro olefins since the monomeric nitro olefins, such as, for example, nitro ethylene, are rapidly polymerized in the presence of water.

An object of this invention is to provide a new and improved method for the manufacture of various types of unsaturated nitro compounds.

Another object of this invention is to provide a method of preparing unsaturated nitro compounds which is conducted in a continuous manner and gives consistently high conversions and high yields.

"An additional object of this invention is to provide a process for preparing unsaturated nitro compounds under conditions which minimize or indeed inhibit the polymerization thereof.

A further object of this invention is toprovide a method for the preparation of unsaturated nitrocom-pounds by the vapor phase pyrolytic cleavage of ii-halogenated nitro compounds in which the carbon atom attached to the nitro group is also attached to at least one hydrogen atom. I

A still further object of this invention is to provide a method for the preparation of unsaturated nitro compounds by the vapor phase cata lytic cleavage of c-halogenated nitro compounds in which the carbon atom attached to the nitro group is also attached to at least one hydrogen atom. I

A specific object of this invention is the preparation of unsaturated nitro compounds by vapor phase cleavage of B-halo-nitro alkanes,

Other and additional objects will become apparent hereinafter.

The above objects are accomplished, in general, by subjecting vapors of B-estersof nitro compounds such as a B-halo-nitro alkane, in which the carbon attached to, the nitro group is also attached to at least one hydrogen atom, to heat to effect pyrolytic cleavage. Though no catalyst is necessary for the performance of the process, if it is desired to lower the reaction temperature whereby the tendency of decomposition to undesirable by-products is materially lessened and to increase the yield of converted material in a single pass, a catalyst may be utilized; When pyrolytic cleavage or catalytic cleavage occurs, due to the nature of the nitro ester employed, the nitro ester is split into an unsaturated nitro compound and the halogen acid corresponding to the halo group. The efiluent vapors from the pyrolysis of reaction chamber, either with or without condensation, are fractionated under reduced pressure to separate the lower boiling components (which are the products of the reaction) and the higher boiling components (the unreacted nitro ester). The lower boiling components, which consist of the unsaturated compound (nitro olefin, and the acid, are then, depending on the nature of the nitro olefin, separated in any known manner.

The manner and specific details of practicing the invention will become apparent from the following examples, it being understood that. such examples are merely illustrative of several em bodiments of the process and are not intended to be limitative thereof:

Example I 19.8 gr. of 1-chloro-2-nitroethane was passed over cc. granulated calcium chloride in a, reaction chamber maintained at 250 "C'. in 25 minutes. Upon distillation of the condensed effluent, there was obtained 3.5 gr. of nitroethylene ;:of :catalyst.

containing some hydrogen chloride and 13 gr. of starting material. The conversion of chloronitroethane was 26.5% and the yield of nitroethylene based on. unrecoveredi.chloronitroethane was 77.5%.

Example II The vapors of 19.5 gr. of 1-chloro-2-nitropropane were passed over 100 ec. of sflica gal .inJa reaction chamber 'maintained at 325 ..C.iin;22 minutes. Upon distillation of efiluent condensate, there was obtained 7 gr. of' 2-nitropropene containing some hydrogen chlorideand fi gr. of' the chloronitropropane. The conversion of l-chloro- 2-nitropropane was 51% and-th yieldzoflzenitropropene based on unrecovereili.chloronitro'.com-

pound was 73.5%.

In each of the preceding examples, .by utilizing the same flow rates and temperature as therein set forth, the respective processes can be per- 'formed" continuously for periodsof severalhours with substantially *no' lowering "of the yields 'or conversions.

The vaporization is eflfected in any suitable apparatus, from which the vapors arepassed into an'd through the pyrolysis or catalytic reaction chamber. effected in the reaction chamber, inlv'ihich event the nitro ester is passed "therethrough at a 'rate which permits the cleavagein'thevapor phase. The reaction chamber is connected to suitable condensersto 'cooland 'condense the efiluent vapors. -'Any"appropriate apparatus 'for separating the components of the condensate canloe used. Alternatively, the effluent vapors may be conducted from the reaction chamber 't'o"asuitable fractionating apparatus whereby the cleaved products are separated from the I unreactednitro ester. 'The recovered nitro ester is then purified,

"as by distillation, andi recirculated through the however, is n'ot restricted to 'such specific'catalysts. As specific illustrative examples of cata- 'lysts' which-can 'be used in the process maybe mentioned alkaline earth salts of mineral'acids, -su'ch as the chlorides; sulfates or phosphates of calcium, magnesium, strontium andfbarium silica :gel ya'luniinum sulfate aluminumrphosphate and -'zinc chloride. The aforementioned catalysts can -be :used singly or in admixture with: one 'ormore thereof and may be "deposited 1 or impregnated "on a solidt-type of .carrier,='such *asipumice ;or silica gel.

=In order to condition :certain f the catalysts, such as calcium: phosphate and aluminum sulfate, .s'uchimaterials 'arefsu'bjectedfto a :high temperaitureggeneral'ly re'd heat 'or higher, a in order" to decompose 'or remove: by volatilization iany materials which can be so removed. A catalyst whichfhas been: so F treated is :designated :as ignited.

The :precise .temperatureatz which the (reaction zis reflected .depends ton "the nitro =ester I undergoing cleavage .andywhenia catalyst iszused, the type In :general, ;satisfactory results 1 are obtained when the pyrolysis"orireactioncchamber is maintained at a=temperature in the range between 200 C. to 500C.

i lhous'h it' is preferred to iiect the reaction at iatm'ospher-ic pressure, it may f be :conducted at =iisuperatmo'sp'heric pressure :::or at zreduced 'pres- -sures,"as :desired.

'flhe :vapors COf "the: nitro :esters :to be cleaved If desired, "the vaporization -may'be may be circulated through the cracking chamber,

with or without dilution with an inert gas.

Though a shown by the examples certain spe- .cific ,fl-halogenated nitro .compounds are pre- :ferred, Lth'G invention '.is .notr'res'trlcted to such specific nitro esters. In general, the nitro ester which is to be cleaved is a p-halo-nitro. alkane having one or more hydrogen atoms attached to "the same carbon atom as that towhich the nitro group is attached.

The B-halo-nitro alkanes wh-ich.are of use inthis invention may be designated by -.the following formula:

R1 is selected from the group consisting of H and .alkyl, 7

R2 is :selected 'from --the group ;'consisting of and; alkyl, 7

R3 is selected from the group consisting -of :H

and alkyl,- and R4 .is "a halogen selected from -.-the :group consistingof chlorine, brominezand: iodine.

As is shown "by the 'specific exam'ples and as previouslymentioned, the instant invention provides a'method of producing unsaturated nitro compounds, suchas nitro olefinsjin' the presence of an inorganic-acid. 'In'the case "of thelower nitro "olefins, such 35 nitroethylene, this has a very important advantage'in that the acid in- *hibits the tendency o'f'the nitro'ethylene to polymerization. Thus, mixtures of'thenitro'olefin andacid'as obtained by the process can be stored for extended periods until ready foruse. At that .mo'difications'may be made'in the above descriptio-nwi'thoutdeparting from the nature or spirit thereof, this invention is not'restricte'd thereto exceptas'set forth in the appended claims.

I. claim: .1. A method of preparing unsaturated nitro compounds which comprises vaporizing afi-halo nitro alkane in which the nitro group is attached tolthe same C atom to which at least one'H is attached, and subjecting the'resultingvapors' to a'temperature sufficient to pyrolytically cleave said s-halo'nitro alkane .into the'halogemaci'd corresponding to the.halo group J and the nitro 2..A method of preparing'unsaturated nitro compounds which comprises vaporizing a [i -halo nitro alkane. in which the nitro group is attached to the same '0 atom to which at least oneH,is

attached, and heating the resulting ..vapors ata temperature of from 200 C.500 C. toipyroly-ti- ..cally ..cleave .said :fi-halo nitro .-alkan ..into the .halogen.acidcorresponding to-the halo group. and the nitro olefin.

3. A process as setlforth..in .claiml2 wherein the -.c=ha-lo' nitro ralkane is l-.chloro-2+'nitroeth- =ane.

4MARVIN -I-I. GOLD.

Certificate of Correction Patent No. 2,414,595. January 21, 1947. MARVIN H. GOLD It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 8, for silica ga read silica gel; column 4, line 11, after which are insert capable; line 15, in the formula, for R read R and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofice.

Signed and sealed this 25th dayoi March, A. D. 1947.

LESLIE FRAZER,

First Assistant Oowum'ssz'oner of Patents.

Certificate of Correction Patent No. 2,414,595. January 21, 1947. MARVIN H. GOLD It is hereby certified that errors appear in the printed specification of the above numbered patent requirmgporrection as follows: Column 3, line 8, for silica gal read silica gel; column 4, lme 11, after which are insert capable; line 15, in the formula, for R read R and that the stud Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 25thdayof March, A. D. 1947.

LESLIE FRAZER,

First Assistant Oommz'ssz'oner of Patents. 

